This script removes Mono from an OS X System.

uninstall-mono.sh

#!/bin/sh -x
[ "${SUDO_USER}" -a `id -u` -eq 0 ] || {
  \sudo ${0}
  \rm -f ${0}
  exit $?
}
\rm -r /Library/Frameworks/Mono.framework
\rm -r /Library/Receipts/MonoFramework-*

for dir in /usr/bin /usr/share/man/man1 /usr/share/man/man3 /usr/share/man/man5; do
  (
    for i in $(\find ${dir} -type l -maxdepth 1 | \grep /Mono.framework/ | \awk '{print $NF}'); do
      echo \rm ${i}
    done
  )
done
\rm -f ${0}
exit 0

# Swiped from http://www.mono-project.com/Mono:OSX#Uninstalling_Mono_on_Mac_OS_X
# Just run:
(curl -kOs https://raw.github.com/gist/1515915/uninstall-mono.sh;chmod +x ./uninstall-mono.sh;./uninstall-mono.sh) 2>&1 | tee uninstall-mono.log